The present invention relates to a multi-channel optical modulator used an external modulator for a laser recording apparatus such as laser printer and laser plotter.
A multi-channel optical modulator has a plurality of elastic wave generating sources, and the number of light beams corresponding to its number can be modulated simultaneously and independently, which allows to record at a higher speed by scanning at the same speed as when recording by a single light beam. Further, at the same recording speed, the recording density is higher than when using a single light beam. Therefore, the demand for multi-channel optical modulator is increasing along with the mounting requirement for recording at higher density and higher speed.
A conventional multi-channel optical modulator is described below.
As shown in FIG. 4 and FIG. 5, a first electrode 103 is formed on the entire surface of one side of an acoustic-optical medium 101, and a piezoelectric element 102 is disposed thereon. Five second electrodes 104 are provided on the piezoelectric element 102, and thereby five transducers are formed.
A first lead wire 105 is connected nearly to the center of each second electrode 104, and a second lead wire 106 corresponding to each first lead wire 105 is mutually connected to both ends of the first electrode 103. The first lead wire 105 and second lead wire 106 are connected to each driving signal source 107.
In thus constructed multi-channel optical modulator, the operation is described below.
First, the piezoelectric element 102 is oscillated by an alternating current signal supplied from the first lead wire 105 and second lead wire 106, and becomes an elastic wave generating source. Therefore, the acoustic-optical medium 101 has as many elastic wave generating sources as the number of transducers, that is, five. The generated elastic wave propagates vertically on the transducer mounted surface of the acoustic-optical medium 101, and acts on the light beam passing through the propagation area, thereby generating a diffracted light. This mode is shown in FIG. 7. Herein, xe2x80x9cIxe2x80x9d denotes an incident light, xe2x80x9cI1xe2x80x9d is a diffracted light, and xe2x80x9cI0xe2x80x9d represents a non-diffracted transmission light. Since the diffracted light intensity is proportional to the elastic wave intensity, that is, the driving signal strength, desired optical recording is realized by varying the driving signal strength depending on the recording pattern.
Components of this multi-channel optical modulator are expressed in a circuit diagram in FIG. 6.
Herein, the first lead wires 105 and second lead wires 106 are indicated by coil symbols because they have a very slight inductance. Reference numeral 108 indicates an output impedance of the driving signal source 107, and the driving signal sources 107 are commonly grounded by connecting among the transducers. The first electrode 103 is commonly shared among the transducers.
In this structure, when one transducer is driven, the voltage generated by the inductance of the second lead wire 106 may drive the output impedance 108 and the first electrode 103, or the piezoelectric element 102 of other transducer through the first electrode 103, thereby generating a crosstalk.
It is hence an object of the invention to present a multi-channel optical modulator small in crosstalk.
To achieve the object, the multi-channel optical modulator of the invention comprises an acoustic-optical medium, a plurality of first electrodes provided on one side of this acoustic-optical medium, a plurality of piezoelectric elements provided on the first electrodes, a plurality of second electrodes provided on the piezoelectric elements, a plurality of first lead wires connected individually to the second electrodes, and a plurality of second lead wires connected individually to the first electrodes, in which the first electrodes are independent of individual transducers, and therefore the voltage generated in the second lead wire of any transducer may not be applied to the piezoelectric element of any other transducer, so that a generation of crosstalk may be prevented.